1. Field of the Invention
The present invention relates to a method and system for making porous silicon and more particularly for fabricating light-emitting silicon devices incorporating porous silicon.
2. Prior Art
Current electrochemical methods for making uniform photoluminescent porous silicon are not readily applicable to silicon (Si) device fabrication because of their complexity and other limitations. For example, highly porous silicon layers formed by electrochemical etching of Si in hydrofluoric acid-based solutions are very useful in photoluminescent and electroluminescent Si devices. However, such porous silicon layers are currently made in complex systems which are not readily adaptable to incorporation in Si device fabrication processes, in that wafers are mounted with one or both surfaces sealed around the edges inside leak-tight chambers in which hydrofluoric acid (HF) solutions are circulated. Some of the limitations of these systems include:
1. high risk of damaging Si surfaces, particularly those with lithographic patterns; PA1 2. prolonged exposure of Si surfaces to HF; PA1 3. non-uniform anodization of the Si surface due to the peripheral seal; PA1 4. Si surface topography and imperfections can result in HF leaks around the seal; PA1 5. in-situ monitoring during anodization is difficult; and PA1 6. system cost is high and wafer throughput is low.
Examples of such systems are found in the Materials Research Society Symposium Proceedings, Light Emmission from Silicon, Boston, Dec. 3-5, 1991.
3. Problem to be Solved
There is therefore a need in the art for a system, having none of these limitations, which is simple to use, low-cost and versatile, and capable of making porous silicon on blank and lithographically or otherwise patterned Si substrates so as to facilitate its use in device fabrication.